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[Octave-bug-tracker] [bug #53397] Delaunay returns inconsistent (cw/ccw)

From: Nicholas Jankowski
Subject: [Octave-bug-tracker] [bug #53397] Delaunay returns inconsistent (cw/ccw) orientations in 2-D (needs overhaul)
Date: Fri, 30 Sep 2022 09:49:30 -0400 (EDT)

Update of bug #53397 (project octave):

                  Status:               Confirmed => Ready For Test         


Follow-up Comment #6:

noting arb's comment #5, this is now actually fairly trivial to implement
since now that the bug #60818 patch made simplex checking for all
dimensionalities consistently calculate the determinant(volume). can
conditionally flip nodes 2 and 3 to change sign of determinant.  checking
against matlab, for many cases where delaunay produces the same simplexes, the
ordering is now identical.  the only one that seems to ignore this is the
trivial 1D case where matlab allows negative oriented vectors in the output. 

implemented with addition of the following to the end of the function: 

if ((dim > 1) && any (negvol = (vol (!idx) < 0)))
  T(negvol, [2, 3]) = T(negvol, [3, 2]);

(could add a dim==1 path in there where it switches 1 and 2, but i don't think
it's necessary. easy enough to add later if anyone objects.)

added a couple BISTs for 2d and 3d.  updated the NEWS paragraph about
delaunayn improvement with this bit.  pushed to default as 
marking as Ready for Test.


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